A genetic analysis of R factors found in, or transmissible to, Pseudomonas aeruginosa is proposed. R factor functions amenable to such an analysis comprise replication, conjugal transfer and its control, the determination of sensitivity to some bacteriophages and resistance to others, surface exclusion and antibiotic resistance. Particular attention will be paid to the conjugal transfer systems of incompatibility group P R factors which are notable in being transmissible to the Enterobacteriaceae as well as Pseudomonas species. Transfer-deficient mutants will be isolated and characterized and used in complementation analysis to identify the transfer cistrons. Derivatives carrying a lambda cI857 prophage inserted into the R factor DNA will be constructed and from these both R factor deletions and transducingg phages for parts of the R factor molecule will be generated. These deletions and transducing phages will be sed to map the genes for the R factor functions listed above. Also, together with prophage insertions within genes, they will be used to elucidate the arrangement of the genes into operons. Ultimately, the physical locations of the genes on the R factor molecule will be determined by electron-microscopical examination of the appropriate heteroduplex molecules. After focusing initially upon one or two P group Pseudomonas R factors, the information gained will be used as a basis for investigating the genetics and biochemistry of the mechanisms by which their fertility is inhibited by other Pseudomonas R factors. Furthermore, the relationships between the transfer systems of the P group R factors and those of other plasmids will be studied. The other plasmids will include further P group R factors, Pseudomonas P factors making related pili but belonging to different incompatibility groups, and plasmids of the F, I, N and W incompatibility groups. Finally, the reasons for the differences in bacterial host range between the "promiscuous" P group R factors and other Pseudomonas or enterobacterial R factors will be investigated using physico-chemical techniques studied. The other plasmids will include further P group R factors, Pseudomonas R factors.